Informatics Publishing Limited

A. C. Dinesh ¹, N. Maran ¹, A. R. Nambiar ¹, E. Unnikrishnan ¹, C. Jayaprakash ¹

Affiliations
1 Marine Wing, Geological Survey of India, Mangalore, IN

Abstract

No Abstract.

Full Text

   

Saju Varghese ¹, A. C. Dinesh ¹, M. Karthikeyan ¹, G. Drishya ¹, N. M. Shareef ¹

Affiliations
1 OPEC-1, M&CSD, ER, Geological Survey of India, Salt Lake, Kolkata 700 091, IN

Abstract

Crustal growth and stabilization in the Andaman accretionary prism (AAP) occur via accretion of allochthonous crust, fragments of oceanic plateaus, and dismembered juvenile arc and ophiolite sequences. Multiple sutures developed in the AAP, as evidenced from multibeam, magnetic and seismic studies, are envisaged as the first-order structures that determine its distinct metallogenic signature. Furthermore, development of Andaman Back Arc Spreading Centre (ABSC) is attributed to a change from compression to more transgression stress regime as the AAP evolves. This stress regime change generates the first-order conduits for episodes of extensive metalliferous fluid flow via the pathways created by significant lateral displacements along the terrane-bounding multiple sutures. Hence, like many other accretionary orogens, complex association between subduction of the Indian plate and associated accretion, deformation, crustal thickening and melting, metamorphism, burial and exhumation may result in a wide variety of magma types, metal source regions and hydrothermal conduits. In conclusion, the expected deposit types in the AAP are volcanogenic massive sulphide deposits, seafloor massive sulphide deposits, rare earth elements and yittrium deposits and podiform chormite deposits.

Keywords

Accretionary Prism, Fluid Migration, Hydrothermal Conduits, Mineral Deposits.

Full Text

   

A. C. Dinesh ¹, N. Maran ¹, K. C. Chandrasekaraiah ², C. Jayaprakash ¹

Affiliations
1 Geological Survey of India, Marine & Coastal Survey Division, Mangalore - 575 001, IN
2 Op. Karnataka and Goa, Bangalore - 560 078, IN

Abstract

Fourteen beach samples were collected between Uvary in the northeast and Kanyakumari in the southwest within a coastal stretch of 50 km were studied to confirm the reported occurrence of micro-diamonds in Pulimankulam beach sands. The XRD results suggest that grains with brilliant luster are mainly zircon and the presence of microdiamond could not be ascertained in any of the samples. The fusion of samples with NaOH and further digestion in acid did not leave any residue. This also confirms absence of any non-silicate mineral in the samples.

Keywords

Micro-Diamonds, Beach Placers, Kanyakumari, Tamil Nadu.

Full Text

     

A. C. Dinesh ¹, N. V. Nisha ¹, Rachna Pillai ¹

Affiliations
1 Marine and Coastal Survey Division, Geological Survey of India, Mangaluru 575 001, IN

Abstract

The economic heavy mineral suite in beach, dune and offshore sands of Odisha, Andhra Pradesh (AP), Tamil Nadu (TN) and Kerala coasts in India mainly comprises ilmenite, garnet, sillimanite, rutile, monazite and zircon. The garnet collected from Kalingapatnam coast, AP reported high incidence (point analysis by EPMA) of rare earth elements (REE) (1500–5300 ppm) especially HREE¹. EPMA of a few garnet grains collected off Anjengo, Kerala, also showed encouraging REE (1200–5000 ppm) values². Nine sand samples were collected from Taingapatnam, Nanjam, Manavalakurichi, Kanyakumari and Uvary in TN, and Santepalle, Bhavanapadu and Yarada in AP (Figure 1) from Indian coast to understand the REE concentrations in garnets. Among the nine, seven samples, viz. GRT-1 (ST-216), GRT-2 (ST-171), GRT-3 (ST-171), GRT-5 (SS-106), GRT-6 (SS-106), GRT-7 (SS-140) and GRT-8 (SS-140) were collected during cruises of Marine and Coastal Survey Division (MCSD), Geological Survey of India (GSI) and the remaining two samples, viz. GRT-10 and GRT-11 were collected from IREL Research Centre, Kollam and AMD, Thiruvananthapuram respectively. These samples contain economically important heavy minerals in different proportions and were subjected to multiple processes for enriching garnet at IREL Research Centre, Kollam, using REDMS (rare earth drum magnetic separator), CSS (corona static separator), EPS (electrostatic plate separator), IRMS (induced roll magnetic separator) and diiodomethane (3.3 specific gravity) to make the samples >95% enriched in garnet. The enriched garnet samples were subjected to HR-ICPMS and XRD analyses for trace elements and mineral phases respectively, at the National Institute of Oceanography (NIO), Goa.

Full Text

   

A. C. Dinesh ¹, N. V. Nisha ¹, Saju Varghese ¹, Rachna Pillai ¹, Durga Prasad ², Satyendra Baraik ³, Rajani P. Ramesh ¹, Rajesh Kumar Joshi ⁴, Soibam I. Meitei ⁴, B. K. Jishnu ¹, R. V. Manoj ⁴, M. Nagasundaram ⁴

Affiliations
1 Geological Survey of India, Op: WC-I, Southern Region, Mangalore 575 001, IN
2 Geological Survey of India, Eastern Region, Kolkata 700 091, IN
3 Geological Survey of India, Southern Region, Op: EC-II, Vishakhapatnam 530 018, IN
4 Geological Survey of India, Eastern Region, Op: EC-I, Kolkata 700 091, IN

Abstract

A reconnaissance survey for Fe–Mn crusts and nodules from West Sewell Ridge (WSR) and Sewell Rise (SR) in the Andaman Sea revealed their widespread occurrence along the summit of the ridge and on the slopes. Remotely operated vehicle (ROV) dive observations illustrate that the crusts are more concentrated on massive exposures at water depth of 800– 900 m and nodules swamped in foraminiferal ooze at water depth from 600 to 1100 m. During the ROV dives, massive, smooth, macro-botryoidal, flat, granular, gritty, coarse and knobby nature of Fe–Mn crusts and nodules have been observed. Nodules and crusts collected onboard were mostly black, brownish-black and pitch black in colour. Nodules show rough, botryoidal and granular/sacchoroidal texture. The diameter of the nodules increased up to 13 cm. They showed distinctly arranged concentric layers. The recovered crusts were mostly detached pieces without substrate.

Keywords

Fe–Mn Crusts and Nodules, Reconnaissance Survey, Rare Earth Elements, Remotely Operated Vehicle, Seamounts.

Full Text